\documentclass{article}

\usepackage{pgfplots}

\pgfplotsset{compat=1.9}

\begin{document}

\begin{tikzpicture}
\begin{axis}[mesh/ordering=y varies,
		view={0}{90},
		enlargelimits=false,]
    % this yields a 3x4 matrix in colwise ordering:
    \addplot3[surf,mesh input=image] coordinates {
        (0,0,0) (0,1,0)   (0,2,0)

        (1,0,0) (1,1,0.6) (1,2,0.7)

        (2,0,0) (2,1,0.7) (2,2,0.8)

        (3,0,0) (3,1,0.5) (3,2,0.5)
    };
\end{axis}
\end{tikzpicture}

\end{document}

